Insertion of alkynes into Pt–X bonds of square planar [PtX₂(N^N)] (X = Cl, Br, I) complexes

Abstract

The reactivity with acetylene of [PtX2(Me2phen)] (X = Cl, Br, I) complexes has been investigated. Whereas the chlorido species [PtCl2(Me2phen)] exhibits negligible reactivity at short reaction times, the bromido and iodido species [PtBr2(Me2phen)] and [PtI2(Me2phen)] lead initially to formation of Pt(II) five-coordinate complexes, [PtX2(η(2)-CH≡CH)(Me2phen)], that evolve to four-coordinate alkenyl complexes of the type [PtX(η(1)-E-CH=CHX)(Me2phen)]. The alkenyl complexes, in the presence of excess acetylene, establish an equilibrium with the five-coordinate alkyne-alkenyl species [PtX(η(1)-E-CH=CHX)(η(2)-CH≡CH)(Me2phen)] (X = Br, I). The π-bonded acetylene can be exchanged with free olefins or C≡O, affording the new alkene-alkenyl or carbonyl-alkenyl complexes [PtX(η(1)-E-CH=CHX)(η(2)-olefin)(Me2phen)] and [PtX(η(1)-E-CH=CHX)(C≡O)(Me2phen)]. The five-coordinate geometry of the alkyne-alkenyl and alkene-alkenyl complexes was assessed from NMR data and is fully consistent with that of a previously determined X-ray structure of [PtBr(η(1)-E-CH[double bond, length as m-dash]CHBr)(η(2)-CH2=CH2)(Me2phen)].

Photoinduced Biphasic Hydrogen Evolution: Decamethylosmocene as a Light‐Driven Electron Donor

“…From the first reports on platinum(II) five‐coordinate complexes, with unsaturated ligands, of the type [PtXY(η 2 ‐alkyne)(∩ NN )]1 and [PtXY(η 2 ‐alkene)(∩ NN )],2–4 ∩ NN = bis‐nitrogen ligand, X, Y = axial ligands (Scheme ), a spectacular growth of knowledge on the chemistry of such complexes has been achieved 5–16. Although some very stable pentacoordinate complexes are well known,17–20 [PtXY(η 2 ‐alkyne)(∩ NN )] and [PtXY(η 2 ‐alkene)(∩ NN )] complexes generally undergo characteristic decomposition patterns, including loss of alkyne or alkene, loss of an axial ligand, chelate ring opening, reductive elimination, and insertion of the unsaturated ligand into a σ‐bond 18.…”

“…Although some very stable pentacoordinate complexes are well known,17–20 [PtXY(η 2 ‐alkyne)(∩ NN )] and [PtXY(η 2 ‐alkene)(∩ NN )] complexes generally undergo characteristic decomposition patterns, including loss of alkyne or alkene, loss of an axial ligand, chelate ring opening, reductive elimination, and insertion of the unsaturated ligand into a σ‐bond 18. In this context, the main decomposition pattern generally involves the formation of reactive cationic intermediates of the type [PtX(η 2 ‐alkyne)(∩ NN )] + and [PtX(η 2 ‐alkene)(∩ NN )] + , respectively (Scheme ) 5,17–19…”

Hindrance, Donor Ability of Men∩NN Chelates and Overall Stability of Pentacoordinate [PtCl2(η2‐CH2=CH2)(Men∩NN)] Complexes as Observed by η2‐Olefin 1JPt,C Modulation: An NMR Study

“…[5,[17][18][19] Previous data and the theoretical description of pentacoordinate complexes, made by Kepert [17,31] and Lin, [32] following the fundamental studies by Hoffmann and coworkers, [33] did not rule out the possibility of thinking of this kind of pentacoordinate complex as particular squareplanar "trans" complexes (pseudo-trans in the following text), where the same coordination position is occupied by the two N-donors. This means that in the Pt II d 8 pentacoordinate complexes, the part of d z 2 electron density, located perpendicular to the square-planar coordination plane, could be considered as lying together with three of the expected filled sp 3 d orbitals on the five-coordinate trigonal equatorial plane.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16] Although some very stable pentacoordinate complexes are well known, [17][18][19][20] [PtXY(η 2 -alkyne)(_ NN)] and [PtXY(η 2 -alkene)(_ NN)] complexes generally undergo characteristic decomposition patterns, including loss of alkyne or alkene, loss of an axial ligand, chelate ring opening, reductive elimination, and insertion of the unsaturated ligand into a σ-bond. [18] In this context, the main decomposition pattern generally involves the formation of reactive cationic intermediates of the type [PtX(η 2 …”

Square‐Planar PtII versus Octahedral PtIV Halido Complexes: 195Pt NMR Explained by a Simple Empirical Approach

“…We recently reported the existence of specific linear relationships between the number and orientation of alkyl groups bonded to coordinated dinitrogen ligands and the observed 195 Pt NMR frequency for pentacoordinate and square‐planar Pt II species , . To better understand the relationship between the observed NMR chemical shifts and the molecular structures of platinum complexes, we studied the Pt II pentacoordinate complexes of the type [PtXY(η 2 ‐olefin)(N^N)] and [PtXY(η 2 ‐alkyne)(N^N)] (X,Y = Cl, Br, I; N^N = dinitrogen ligand). In particular, collection of the 1 H, 13 C, 15 N, and 195 Pt NMR spectroscopic data of the considered pentacoordinate complexes allowed the linear correlation of the chemical shift frequencies with both the spatial disposition of the observed nuclei and the ionic radii of the apical halido ligands (Figure , A) , .…”